to show that in all essential respects they are identical. He was further
able to prove that there is a complete gradation between the highly
crystalline or granitic rock-masses, and those containing more or less
glassy matter between their crystals, which constitute ordinary lavas. The
importance of this conclusion will be realised when we remember that it was
then the common creed of geologists--and still continues to be so on the
Continent--that all highly crystalline rocks are of great geological
antiquity, and that the igneous ejections which have taken place since the
beginning of the tertiary periods differ essentially, in their composition,
their structure, and their mode of occurrence, from those which have made
their appearance at earlier periods of the world's history.

Very completely have the conclusions of Darwin upon these subjects been
justified by recent researches. In England, the United States, and Italy,
examples of the gradual passage of rocks of truly granitic structure into
ordinary lavas have been described, and the reality of the transition has
been demonstrated by the most careful studies with the microscope. Recent
researches carried on in South America by Professor Stelzner, have also
shown the existence of a class of highly crystalline rocks--the
"Andengranites"--which combine in themselves many of the characteristics
which were once thought to be distinctive of the so-called Plutonic and
volcanic rocks. No one familiar with recent geological literature--even in
Germany and France, where the old views concerning the distinction of
igneous products of different ages have been most stoutly maintained--can
fail to recognise the fact that the principles contended for by Darwin bid
fair at no distant period to win universal acceptance among geologists all
over the globe.

Still more important are the conclusions at which Darwin arrived with
respect to the origin of the schists and gneisses which cover so large an